The present invention relates to a turbo-machine, and in particular to a turbo-type hydro machine being able to prevent flow instability from occurring within fluid (in particular, a water including freshwater and seawater), which flows in an inside thereof, by suppressing rotation of an impeller and stalls in rotation thereof due to re-circulation flow at an inlet of the impeller, irrespective of the types and fluid thereof.
In more detail, the turbo-type machine according to the present invention has an impeller of non-voluminous type, and in particular, it relates to a pump or a pump turbine (a turbo-type pump turbine), in which the fluid flowing therein is a liquid (such as, a water including fresh water and seawater). Namely, according to the present invention, it is possible to prevent the flow instability from occurring within the fluid, by suppressing pre-swirl in main flow of the re-circulation at an inlet of the impeller and/or stalls in rotation of the impeller, and further to reduce generation of cavitations in the impeller, which accompanies increases in vibrations and noises therewith, therefore being suitable for a mixed-flow pump, in particular, which is applicable to a re-circulation water pump, etc., to be used as a drainage pump in a city, or used in a thermal power plant or a nuclear power plant, etc.
FIG. 13 shows a typical characteristic curve between head and flow rate in the turbo-machine of the conventional art, including the mixed-flow pump shown in FIG. 14 therein, where the horizontal axis is a parameter indicative of a flow rate, while the vertical axis a parameter indicative of the head. Namely, the head falls down in a reverse relation to increase of the flow rate in a region of low flow rate, however it rises up following the increase of the flow rate during the time when the flow rate lies within a xe2x80x9cSxe2x80x9d region (i.e., the characteristic of uprising at the right-hand side). And, when the flow rate rises up further, exceeding over the region of uprising at the right-hand side, then the head falls down again. In a case where the turbo-machine is operated at the flow rate with the characteristic curve of uprising at the right-hand side, a mass of the liquid vibrates by itself, i.e., generating a surging phenomenon.
Such the characteristic curve, uprising at the right-hand side on the head-flow rate curve in the conventional turbo-machine mentioned above, is caused since, although the re-circulation comes out at an outer edge on the inlet of the impeller when the flow rate comes to be low in the fluid flowing through the turbo-machine, but at this instance, a flow passage or a channel for the liquid flowing within the turbo-machine is narrowed, thereby generating a swirl in the liquid (see FIG. 14).
For improving the characteristic of such uprising at the right-hand side in the conventional turbo-machine, as is disclosed in, for example xe2x80x9cA New Passive Device to Suppress Several Instabilities in Turbomachines by Use of J-Groovexe2x80x9d (Turbomachine Association, published Nov. 1, 1998) presented in a Japan-US Science Cooperation Business Seminar held on Nov. 1 to 6, 1998, it is already proposed by Mr. Junichi KUROKAWA, who is an inventor of the resent invention, and is already known, to provide a plural number of grooves in an axial direction of the pump (i.e., the direction of pressure gradient in fluid) on an inner surface of a casing of the mixed-flow pump.
In the turbo-machine according to the conventional art mentioned above, an idea of providing the grooves in the axial direction of the pump (i.e., the direction of pressure gradient in fluid) on the inner surface of the casing is adopted, for improving the characteristic of uprising at the right-hand side in the turbo-machine, however according to the present inventors, it is acknowledged there sometimes occurs a case where the following problems are caused due to the cavitations generated in the casing with such the idea of providing the grooves formed on the inner surface of the casing.
Namely, the cavitations that comes up to the problem is a phenomenon, where a large number of bubbles occur due to evaporation within the liquid when the pressure of the liquid flowing within the pump is decreased down in the vicinity of the saturated vapor pressure, for example, and those bubbles generated flow within the pump, and/or are collapsed accompanying with recovery of the pressure within the pump. And, such the generation of the cavitations gives damages upon wall surfaces of the impeller, as well as the casing, and it may also cause harmful effects, such as, increase in the vibrations and/or noises, and decrease in the performance thereof, as well.
Also, FIG. 15 shows an experimental result of vibration acceleration, as one representative example of the vibrations and/or noises due to influences of the cavitations, wherein the horizontal axis indicates the flow rate without dimension while the vertical axis the vibration acceleration without dimension thereof. In particular, black circles (xe2x97xaf) in the figure show a flow rate-vibration acceleration curve in a condition where the pump is high in NPSH, in which no groove is formed on the casing thereof, white circles (◯) in a condition where the pump is low in NPSH, in which no groove is formed on the casing thereof, black triangles (▴) in a condition where the pump is high in NPSH, in which the grooves are formed on the casing in the direction of pressure gradient, and white triangles (xcex94) in a condition where the pump is low in NPSH, in which the grooves are formed on the casing in the direction of pressure gradient, respectively. Herein, the NPSH means an effective suction head, and it indicates how much higher a total pressure, which the liquid upon a standard surface of the impeller has, than the saturated vapor pressure of that liquid at that temperature. Namely, the lower the NPSH, the nearer to the saturated vapor pressure, i.e., it comes to the condition where the cavitations can easily occur therein.
As shown in the FIG. 15, in the pump in which no groove is formed on the casing thereof, comparing the black circles (xe2x97xaf) of high NPSH to the white circles (◯) of low NPSH, the white circles are as about 1.3 times large as the black ones, at the maximum in the vibrations thereof between xcfx86=0.6-1.0, but it does not matter in particular. However, with the black triangles (▴) and white triangles (xcex94) indicating the characteristic curves of the pumps, in which the grooves are formed on the inner surface of the casing in the direction of pressure gradient (i.e., the axial direction), as is apparent from the figure, when comparing the black triangles of high NPSH to the white triangles of low NPSH, the white triangles of low in the NPSH of the pump comes to be about as 2.1 times large as the black ones, at the maximum in the vibration thereof between xcfx86=0.6-1.0, and there can be sometimes found cases where the vibrations and/or noises are increased extraordinarily.
A reason of this can be explained as below, upon the basis of an observation of the condition in generating the cavitations within the pump, and an analysis of turbulences in the flow within the pump in a case where no such the cavitations occurs.
Namely, with the impeller of a small outer diameter for aiming at small-sizing of the pump, a load upon a blade is large, therefore a pressure difference between a negative pressure surface and a pressure surface of the blade comes to be large, and in a case where the NPSH is low, the cavitations 4 occurs in an aperture or gap 3 between the blades 122 of the impeller and the casing, as shown in FIGS. 16 and 17. However, the FIG. 16 shows a view of the inner surface of the casing, on which the grooves 124 are formed, being expanded schematically, and the FIG. 17 a cross-section view of the blade of the impeller, being cut by a horizontal cross-section perpendicular to a pump axis thereof. The cavitations 4 occurring in this gap 3 develops up to the negative pressure side of the blade 122, and a rear end of the cavitations reaches up to the grooves 124 mentioned above.
While, as shown in FIG. 18, within the groove 124, the flow 51 of the fluid directing from the impeller to an upstream side is opposite to flow 52 of the fluid entering from the upper stream into the impeller, therefore there occurs a region where the flow stands still within the groove 124. Further, if the cavitations 4 reach up to such the region, the cavitations do not flow away from but stays within the groove, and they are collapsed therein. And, due to the collapse of the cavitations, large noises and/or vibrations are brought about within the pump.
The present invention is made, as was mentioned in details thereof in the above, in consideration of the problem, such as the cavitations, which may occur with the provision of the grooves formed on the inner surface of the casing for dissolving the head-flow rate characteristic of uprising at the right-hand side. Namely, an object according to the present invention is to obtain a turbo-machine, having a head-flow rate characteristic of no such the uprising at the right-hand side, at the same time suppressing the increase of the vibrations and/or the noises therein.
For accomplishing the object mentioned above, according to the present invention, there is provided a turbo-type machine, comprising: a casing for storing an impeller having blades within an inside thereof; and a plural number of grooves formed on an inner surface of said casing, connecting between an inlet side of the blades and an area on said inner surface where the blades exist, in a direction of pressure gradient of fluid, wherein said grooves are provided in plural from 80 to 150 pieces around a periphery on the inner surface of said casing, and further a total width of said grooves all around the inner surface of said casing is set to be from 30% to 50% with respect to a peripheral length on the inner surface of said casing.
According to such the structure of the turbo-type hydro machine, instable flow of fluid at a terminal end of cavitations, which are generated in a gap at the tip of the blades and enter into the grooves, is guided through a large number of grooves mentioned above, so as to be stabilized therewith, therefore it is possible to mitigate the vibrations and/or noises accompanying with collapse of the cavitations.
Also, according to the present invention, there is provided a turbo-type machine, comprising: a casing for storing an impeller having blades within an inside thereof; and a plural number of grooves formed on an inner surface of said casing, connecting between an inlet side of the blades and an area on said inner surface where the blades exist, in a direction of pressure gradient of fluid, wherein, a cross-section area of said grooves within the area where the blades exist are set to be larger than that of said grooves within an area outside where the blades exist. With constructing it in this manner, it is possible to reduce the vibrations and/or noises due to the cavitations caused in the gap at the tips of the blades.
Further, according to the present invention, there is provided a turbo-type machine, comprising: a casing for storing an impeller having blades within an inside thereof; and a plural number of grooves formed on an inner surface of said casing, connecting between an inlet side of the blades and an area on said inner surface where the blades exist, in a direction of pressure gradient of fluid, wherein said grooves are disposed in unequal distances around a periphery on the inner surface of said casing. With constructing it in this manner, since the grooves mentioned above are, not arranged in uniform at an equal distance in the inner peripheral direction of the casing, but are in unequal distances, therefore fluctuations in pressure caused by a kind of an interference between the impeller rotating and flow passages of the grooves standing still becomes irregular, therefore it is possible to suppress the cavitations to stay within the grooves periodically, thereby reducing the vibrations and/or noises due to the cavitations.
Also, according to the present invention, there is provided a turbo-type machine, comprising: a casing for storing an impeller having blades within an inside thereof; and a plural number of grooves formed on an inner surface of said casing, connecting between an inlet side of the blades and an area on said inner surface where the blades exist, in a direction of pressure gradient of fluid, wherein one portion of said plural number of grooves are formed to be uniform in a shape of cross-section thereof in an axial direction of said casing, while other portion of said plural number of grooves are formed to be different in the shape of cross-section thereof from that in the area where the blades exist, and said one portion of grooves and said other portion of grooves are disposed alternately.
Also, in the turbo-type machine mentioned above, it is possible to make the area of cross-section of the groove of the above-mentioned other portion larger than that of the grooves of the one portion mentioned above. For example, while the groove of the one portion is made uniform in the shapes of axial direction thereof, the groove of the other portion is made smaller in the width and larger in the depth than those of the above in the area where the blades exist, and they are positioned alternately or one by one, thereby making the flow of fluid in the grooves, not uniform, but rather be different to one another. Namely, the cavitations generated are made different in shapes thereof, thereby mitigating the vibrations and/or noises when the collapse thereof occurs.
Further, according to the present invention, there is provided a turbo-type machine, comprising: a casing for storing an impeller having blades within an inside thereof; and a plural number of grooves formed on an inner surface of said casing, connecting between an inlet side of the blades and an area on said inner surface where the blades exist, in a direction of pressure gradient of fluid, wherein openings are drilled on said grooves, each penetrating from a bottom surface thereof through thickness of said casing, in a portion near to a front edge of the blade within the area where no blade exist, and further is provided a ring-like chamber on an outer peripheral surface of said casing, wherein said ring-like chamber is conducted to a position in a stream upper than said penetrating openings in said casing. In this manner, the conducting the grooves to the ring-like chamber on the outer periphery of the casing suppresses the stay of the cavitations, thereby suppressing the generation of the cavitations.
Further, according to the present invention, there is provided a turbo-type machine, comprising: a casing for storing an impeller having blades within an inside thereof; a suction inlet, being dipped within fluid to be transferred, together with at least said casing; and a plural number of grooves formed on an inner surface of said casing, connecting between an inlet side of the blades and an area on said inner surface where the blades exist, in a direction of pressure gradient of fluid, wherein, openings are drilled on said grooves, each penetrating from a bottom surface thereof through thickness of said casing, in a portion near to a front edge of the blade within the area where no blade exist. With such the construction, conducting the grooves to a water tank, in which a pump is dipped into, for example, suppresses the stay of the cavitations, thereby suppressing the generation of the cavitations.
Further, according to the present invention, there is provided a turbo-type machine, comprising: a casing for storing an impeller having blades within an inside thereof; and a plural number of grooves formed on an inner surface of said casing, connecting between an inlet side of the blades and an area on said inner surface where the blades exist, in a direction of pressure gradient of fluid, wherein said grooves is so set in length thereof within said area where the blades exist, that each of the blades of said impeller intersects with at least one piece or more of said grooves on an inner surface of said casing, irrespective of any position of said blade in a peripheral direction. With constructing it in this manner, since each of the grooves always intersects with at least one piece or more of the blades irrespective of any position of the blades, it is possible to make the difference large between the pressure at a terminal end of the groove at the side of the impeller and the pressure at a start end thereof at the side of suction. With this, the flow flowing through the grooves is increased up, thereby suppressing the cavitations to stay within the grooves, and suppressing the increase of the vibrations and/or noises due to the cavitations.
Further, according to the present invention, there is provided a turbo-type machine, comprising: a casing for storing an impeller having blades within an inside thereof; and a plural number of grooves formed on an inner surface of said casing, connecting between an inlet side of the blades and an area on said inner surface where the blades exist, in a direction of pressure gradient of fluid, wherein each of said grooves is made in a two-layer structure in the direction of said pressure gradient of fluid, whereby reverse flow from said impeller passes through a layer formed on a side deep with respect to the inner surface of said casing, while main flow directing to said impeller passes through a layer formed on a side shallow with respect to the inner surface of said casing. Namely, the grooves are constructed so that no collision occurs between the main flow and the reverse flow within the grooves, thereby suppressing the stay of the cavitations within the grooves.
In addition to the above, according to the present invention, there is provided a turbo-type machine, comprising: a casing for storing an impeller having blades within an inside thereof; and a plural number of grooves formed on an inner surface of said casing, connecting between an inlet side of the blades and an area on said inner surface where the blades exist, in a direction of pressure gradient of fluid, wherein a round portion having a radius from 1/4 to 1/2 of thickness of said blade is formed on a ridge defined by a pressure surface and an outer peripheral surface in a direction of thickness thereof, at a tip of each blade of said impeller. Namely, the round portion having the radius from 1/4 to 1/2 of the thickness of blade is provided at the front edge on the side of pressure surface of the blade, thereby suppressing the cavitations to generate from the front edge of the blade.
Also, according to the present invention, there is further provided a turbo-type machine, comprising: a casing for storing an impeller having blades within an inside thereof; and a plural number of grooves formed on an inner surface of said casing, connecting between an inlet side of the blades and an area on said inner surface where the blades exist, in a direction of pressure gradient of fluid, wherein a fin is formed at each tip of said blades of said impeller in a peripheral direction thereof, extending in a direction on side of a negative pressure surface of said blade by a width from 1/4 to 1 of thickness of the blade. Namely, the fin having the width from 1/4 to 1 of thickness of the blade is provided at the tip on the negative pressure surface of the blade, thereby not only suppressing leaking flow in the gap at the tip of the blade, but also suppressing the generation of cavitations.
Other feature(s), object(s) and/or advantage(s) of the present invention will be apparent from the following explanation given below by referring to the attached drawings.